JP3589773B2 - Radio receiver noise elimination circuit. - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a noise removal circuit for a radio receiver that receives multi-frequency bands such as an AM band and an FM band.
[0002]
[Prior art]
FIG. 3 is a configuration diagram showing a circuit configuration of a conventional radio receiver for receiving an AM band and an FM band with a noise removal circuit.
Reference numeral 1 denotes an AM band receiving unit, which comprises a semiconductor integrated circuit and its peripheral parts, and a high frequency amplifier 13 for amplifying an AM carrier input from an antenna (ANT), and a frequency converter 14 for converting the output signal to an intermediate frequency. , An intermediate frequency amplifier 15 for band-amplifying the intermediate frequency signal, and an AM detector 16 for AM detection of the output signal.
[0003]
Reference numeral 2 denotes an AM gate, which is composed of a semiconductor integrated circuit, a transistor, or the like which cuts off an audio signal output from the AM detector 16 by electronic control (driven by a rectangular wave), and always passes (outputs) the signal in a conductive state. The gate 2 is cut off by detecting pulse-like noise.
Reference numeral 3 denotes a noise component detection unit for AM reception, which is an AGC controlled circuit 17 for branching and inputting the intermediate frequency signal output from the frequency converter 14 and adjusting the automatic gain of the noise component detection unit 3; An intermediate frequency amplifier 18 having a required gain and bandwidth, a noise component detector 19 for detecting a pulse noise component, and a gate drive circuit 20 for shaping the noise component and driving and controlling the gate 2 It is configured.
[0004]
Reference numeral 4 denotes a waveform compensating circuit, which includes an integrating circuit and the like, and is provided so that when the signal output from the AM gate 2 has a discontinuous waveform, the signal becomes a continuous waveform.
Reference numeral 5 denotes a power amplifier that amplifies a signal from an audio signal subjected to AM detection or FM stereo (MPX) demodulation and drives a speaker, and 6 denotes a speaker that outputs audio.
[0005]
Reference numeral 7 denotes an FM band receiving unit, which comprises a semiconductor integrated circuit and its peripheral parts, and a high frequency amplifier 21 for amplifying an FM carrier input from an antenna (ANT), a frequency converter for converting the output signal to an intermediate frequency and an intermediate frequency. It comprises an intermediate frequency amplifier 22 for band-amplifying the frequency signal, and an FM detector 23 for FM detecting the output signal.
[0006]
Reference numeral 8 denotes a low-pass filter (LPF) which includes a resistor, a capacitor, a transistor, and the like, delays a noise pulse from the FM detector 23, and outputs the delayed noise pulse to the FM gate 9.
Reference numeral 9 denotes an FM gate, which is composed of a transistor or the like that cuts off a composite signal output from the LPF 8 by electronic control (driven by a rectangular wave), and always passes the signal as a conductive state, in response to input of pulse noise. , The gate 9 is shut off.
[0007]
Reference numeral 10 denotes a noise component detection unit for receiving an FM band, a high-pass filter (HPF) 24 that passes high frequency components including noise from the composite signal output from the FM detector 23, and a high frequency component of the composite signal. An AGC circuit 25 for amplifying and automatically adjusting the gain, a noise detector 26 for detecting a noise pulse from this high frequency component, and a gate drive circuit 27 for shaping the detected noise pulse and driving the gate 9. It is composed of
[0008]
Numeral 11 denotes a waveform compensating circuit which is composed of an integrating circuit or the like, and is provided so that when the signal output from the FM gate 9 has a discontinuous waveform, it becomes a continuous waveform.
An FM stereo (MPX) demodulator 12 demodulates the composite signal output from the waveform compensation circuit 11 into a stereo signal.
[0009]
Next, the operation will be described.
The pulse noise radio waves generated from the ignition system of the engine and the like are spread in terms of both their large energy and wide frequency range, and are liable to cause radio reception failure. In a situation where the ratio becomes a problem (a weak electric field or a medium electric field), a radio reception failure is particularly likely to occur, and therefore, a noise removal circuit is used on the radio receiver side.
[0010]
First, AM reception and pulse noise removal will be described.
An output obtained by superimposing a carrier signal of AM broadcast from an antenna (ANT) and a pulse noise generated from an ignition system of an engine or the like is amplified by a high-frequency amplifier 13 which is a first stage of the AM receiving unit 1, and transmitted to a frequency converter 14. Is output.
The frequency converter 14 converts the signal into an intermediate frequency, and the audio signal and noise pulse, which are AM modulated components, are detected by the AM detector 16 via the intermediate frequency amplifier 15 and output to the AM gate 2.
[0011]
On the other hand, the signal and the noise wave converted to the intermediate frequency by the frequency converter 14 are output to the AGC controlled circuit 17 in the first stage of the AM band noise detection unit 3 and the frequency band in which the intermediate frequency amplifier 18 responds to the noise pulse. The signal is amplified by the width, the noise component is detected from the noise detector 19, and output to the gate drive circuit 20.
By sending a gate control signal formed in accordance with the detected noise component to the controlled terminal of the AM gate 2, the noise pulse appears on the input side of the AM gate 2 for a short period corresponding to the pulse. The AM gate 2 is cut off, during which no noise and voice signal appear on the output side of the AM gate.
[0012]
The output signal of the AM gate 2 is compensated for by the waveform compensation of the waveform compensating circuit so that the sense of incongruity caused by the intermittent sound signal is reduced.
Next, FM reception and pulse noise removal will be described.
The output in which the carrier signal of the FM broadcast from the antenna (ANT) and the pulse noise generated from the ignition system of the engine and the like are superimposed is amplified by the high-frequency amplifier 21 which is the first stage of the FM receiving unit 7 and frequency-converted to an intermediate frequency. Output from an intermediate frequency amplifier 22 that amplifies the intermediate frequency signal, and is detected by an FM detector 23. The composite signal and the noise are superimposed on each other, output, and filtered and delayed by a low-pass filter (LPF) 8. , FM gate 9.
[0013]
On the other hand, the composite signal and the noise detected by the FM detector 23 are input to a high-pass filter (HPF) 10 at the first stage of the noise detection unit 10 for FM reception, where the noise pulse component is filtered, and the AGC-equipped amplifier 25. And a noise pulse component ranging from a small amplitude to a large amplitude is amplified to a substantially constant amplitude.
Then, the noise pulse is input to the noise detector 26, the noise pulse is detected, and the noise pulse is input to the gate drive circuit 27. The noise pulse is shaped into a fixed pulse width at a cycle corresponding to the noise pulse and transmitted to the controlled terminal of the FM gate 9. Thus, the FM gate is shut off for a short period of time when the noise pulse appears at the input side of the FM gate 9, so that noise and a composite signal do not appear at the output side of the FM gate 9.
[0014]
The partial loss of the composite signal due to the cutoff of the FM gate is compensated by a waveform compensating circuit, and the output is input to a stereo demodulating circuit 12, where it is demodulated into an audio signal without pulse noise and amplified by a power amplifier 5. The sound is output from the speaker 6.
[0015]
[Problems to be solved by the invention]
As described above, the AM receiver and the FM receiver each include a noise removing circuit, and are radio receivers having a high level of noise immunity, but still have the following problems.
For example, at the time of AM broadcast reception, especially in a certain reception area at night, the operation of the gate of the noise removal circuit due to strong adjacent waves or fading is frequently performed, so that the received audio signal is distorted, The sound quality may be extremely deteriorated.
[0016]
SUMMARY OF THE INVENTION It is an object of the present invention to provide a noise elimination circuit of a receiver free from such distortion of an audio signal.
[0017]
[Means for Solving the Problems]
The present invention relates to a radio receiver with a noise elimination circuit having a plurality of receiving units for receiving a plurality of frequency bands, and detects a noise component from a receiving unit in another frequency band different from the receiving frequency band. And a means for disconnecting a signal path by using an output of the noise detecting means, wherein the noise detecting means detects a frequency outside a band near an upper limit or a lower limit of the FM band during reception of the AM band. And detecting a noise component from the data.
[0019]
【Example】
Next, examples of the present invention will be described.
FIG. 1 is a configuration diagram showing a circuit configuration of an embodiment of the present invention.
Note that the same circuit configurations as those of the conventional radio receiver shown in FIG. 3 are denoted by the same reference numerals, and description thereof will be omitted.
[0020]
Reference numeral 28 denotes an envelope detector which includes a transistor, a diode, a capacitor, a resistor, and the like, and outputs an intermediate frequency output from the intermediate frequency amplifier 22 which is a part of a circuit included in the FM receiver 7 from an ignition system of the engine. The amplitude modulation component appearing due to the generated pulse noise or the like is detected over a wide band and output to the noise component detection unit 10.
[0021]
Reference numeral 29 denotes a changeover switch, which is mechanically or electrically linked to a band switch of a so-called radio receiver for selecting the AM band or the FM band, and switches the input system of the noise component detection unit 10 between AM time and FM time. Is configured to perform selection switching.
Reference numeral 30 denotes an AM gate drive circuit for driving the AM gate 2, which is constituted by a one-shot multivibrator, a pulse time adjustment circuit, and the like.
[0022]
Next, the basic operation (reception of broadcasts in the AM and FM bands) of the present embodiment is the same as that of the conventional radio receiver shown in FIG. The operation of the part will be described in detail below.
As a feature of the present embodiment, the receiving unit of the FM band performs an operation of detecting a noise component during reception of the AM band, and the receiving unit of the AM band pauses during the reception of the FM band.
[0023]
First, a case where pulse noise is mixed in from an antenna (ANT) during reception of an AM broadcast in the AM band will be described.
The pulse noise generated from the ignition system of the engine and the like input from the antenna (ANT) is received together with the sound by the AM receiving unit 1, superimposed on the sound by the AM detector 16, and output to the AM gate 2.
[0024]
On the other hand, the pulse noise exists over the wide band, is amplified by the high frequency amplifier 21 of the FM receiving unit 7, is output from the frequency converter and the intermediate frequency amplifier 22, and is input to the envelope detector 28.
This pulse noise is a spectrum corresponding to the pass band characteristic of the intermediate frequency amplifier (10 times or more as compared to the AM band intermediate frequency amplifier), whereby the noise is detected by the envelope detector 28 and has a sharp rising noise. Output as a pulse.
[0025]
Then, the noise pulse is input to the noise detection unit 10 which is set to be shared between the AM band and the FM band via the switch 29, and a gate drive signal corresponding to the pulse noise input from the antenna (ANT) is gate-driven. The output from the circuit 27 is input to the AM gate drive circuit 30.
The AM gate drive circuit 30 outputs a gate drive pulse necessary for removing a noise pulse superimposed on the voice and input to the AM gate to the AM gate 2, and the AM gate 2 outputs the voice and the voice according to the noise pulse. Block out noise pulses.
[0026]
In other words, the pulse width of the noise pulse superimposed on the sound detected by the AM detection is wide, and there is a time delay of the rise of the pulse (according to the band ratio of the intermediate frequency amplifier between the AM band and the FM band). The steep rising noise pulse detected by the envelope detector 28 matches the noise pulse to eliminate the noise pulse, and optimizes the gate cutoff time (pulse width) and the cutoff start time. An AM gate drive circuit 30 is provided so as to form the gate drive pulse and output the same to the AM gate 2, and drives the AM gate 2.
[0027]
Note that the reception frequency of the FM receiving unit 7 during the reception of the AM broadcast is such that the FM broadcast signal does not exist (the driving pulse for driving the AM gate is not affected by the FM broadcast wave), and 10 requires a representative FM reception frequency suitable for detecting only pulsed noise, which is near the upper or lower limit of the FM broadcast band, and outside of that band (eg, 75.5 MHz or 91.5 MHz). 0 MHz).
[0028]
In the case where both the AM band and the FM band reception frequencies are controlled simultaneously by the microcomputer, the size of the microcomputer and its peripheral circuits is approximately doubled.
Therefore, as a solution to this problem, a method of fixing the reception frequency without using a microcomputer will be described with reference to FIG.
[0029]
FIG. 2 is a circuit diagram showing an embodiment of a method for fixing an FM reception frequency during reception of an AM broadcast by an electronic tuning receiver.
Reference numeral 51 denotes a frequency control local oscillator (VCO) for the FM band, which is included in the frequency converter 22 and uses a variable capacitance diode as an oscillation circuit, and varies the DC bias voltage of the diode to vary the oscillation frequency. .
[0030]
Reference numeral 52 denotes a changeover switch which selects the AM band or the FM band, and is electrically linked with the switches 29 and 31.
Numeral 53 denotes a semi-fixed potentiometer which divides the stabilized DC voltage and supplies it to the VCO 51 as a tuning bias voltage (frequency control voltage) for the diode of the VCO 51.
[0031]
During the AM band reception, the frequency control voltage of the VCO 51 is supplied from the potentiometer 53 via the contact AM of the switch 52, and by adjusting the potentiometer, the reception frequency of the FM band is set to a predetermined frequency (for example, 75.5 MHz). Fixed and set.
During reception in the FM band, the operation is the same as that of the related art, and the frequency control voltage of the VCO 51 is connected to a low-pass filter or a microcomputer (not shown) via the contact FM of the switch 52, and is controlled (phase-locked loop control). You.
[0032]
As described above, according to the present embodiment, in the AM band reception, the noise detection of the pulse noise elimination circuit is performed not in the AM band but in the FM band. Distortion of the audio signal due to improper operation of the elimination circuit is resolved.
Further, it is possible to reduce the number of noise detection units from the conventional two systems for the AM band and the like to the FM band to one system, which can contribute to downsizing of a printed circuit board constituting a radio and cost reduction.
[0033]
The operation of the pulse noise processing in the FM band is the same as the circuit configuration of the conventional receiver shown in FIG. 3, and the description is omitted.
[0034]
【The invention's effect】
As described in detail above, according to the present invention, distortion of an audio signal can be reduced by detecting noise from a frequency band other than the reception frequency.
[Brief description of the drawings]
FIG. 1 is a configuration diagram showing a configuration of an embodiment of the present invention.
FIG. 2 is a diagram showing an example of a method of setting an FM reception frequency during AM reception.
FIG. 3 is a configuration diagram showing a circuit configuration of a conventional radio receiver.
[Explanation of symbols]
1 AM band receiving unit 2 AM gate 3 AM band noise detecting unit 4 Waveform compensating circuit 5 Power amplifier 6 ... Speaker 7 ... FM band receiver 8 ... Low-pass filter (LPF)
9 FM gate 10 FM band noise detector 11 Waveform compensation circuit 12 FM stereo (MPX) demodulator 13 High frequency amplifier 14 Frequency converter 15 intermediate frequency amplifier 16 AM detector 17 AGC controlled circuit 18 intermediate frequency amplifier 19 noise detector 20 Gate drive circuit 21 High-frequency amplifier 22 Frequency converter and intermediate frequency amplifier 23 FM detector 24 High-pass filter (HPF)
25 Amplifier with AGC 26 Noise detector 27 Gate drive circuit 28 Envelope detector 29 Switching switch 30 AM gate drive circuit

Claims (1)

In a radio receiver with a noise removal circuit having a plurality of receiving units that receive a plurality of frequency bands,
Noise detection means for detecting a noise component from the receiving unit in another frequency band different from the frequency band being received;
Means for disconnecting the signal path using the output of the noise detection means,
A noise removing circuit for a radio receiver, wherein the noise detecting means detects a noise component from a frequency outside a band near an upper limit or a lower limit of an FM band while receiving an AM band.

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